Dial bore gages are specifically used to determine if the diameter and surface characteristics of cylindrical holes or bores are accurate to some known standard and such gages include gaging head members which gage the surface and have portions operatively connected to dial indicator means which indicate the condition and size of the hole or bore. Such dial bore gages are generally set and calibrated prior to usage based upon the final desired size or diameter of the bore to be gaged so that a user may quickly and accurately determine if the diameter and surface characteristics of such bore are of the desired size and finish, or if the diameter and surface finish is off by some amount, and if so, whether the bore is over or under size. This calibration is usually accomplished by placing the dial bore gage on a setting fixture, the setting fixture providing holding and supporting means for adjusting the alignment of the gaging contacts associated with the probe tip of a particular dial bore gage to the setting surfaces associated with the setting fixture. This procedure establishes the precise known distance between the gaging contacts and, based upon this known standard, the diameter and surface characteristics of a particular cylindrical hole or bore may be gaged. Typical of known setting fixtures is the fixture disclosed in Sunnen U.S. Pat. No. 3,496,758 and the gage support means disclosed in co-pending Rutter et al U.S. patent application Ser. No. 142,192, filed Jan. 11, 1988.
Once the gaging contacts associated with a particular dial bore gage have been set and calibrated, it is generally desired to reposition the movable pointers associated with the dial indicator to a zero setting to facilitate easy reading of the dial indicator to determine if the diameter and surface characteristics of the bore to be gaged are of the desired size and finish. If the gaging contacts are set to the desired finished size of the bore to be gaged as previously explained and the dial indicator reads zero, then, when the gage is positioned within the particular bore for the gaging thereof, the bore diameter will, if proper size, correspond to the desired finish diameter set between the gaging contacts. A reading other than zero on the dial indicator such as a plus or minus reading on the dial face indicates that the particular bore is either over or under size.
Adjusting the movable pointers of the dial indicator to a zero reading has been accomplished in the past by using one of several known means. For example, zeroing of the dial indicator may be accomplished by either slidably or rotatably moving the dial indicator face so as to align the zero index marking on the dial with the dial pointer, or by otherwise moving the indicator stem associated with the particular gage to reposition the movable pointer over the zero index marking. It is an advantage to be able to zero the movable pointer associated with the dial indicator prior to usage for various reasons including for convenience purposes and for ease of reading the dial indicator during a gaging process. Typical of the known dial setting means are the means disclosed in U.S. Pat. Nos. 4,045,877; 4,476,634 and 4,477,977.
None of the known means for zeroing a dial indicator to a preset diameter of the probe tip makes such an adjustment between the probe tip and the dial portion independent of any outside means such as a setting fixture as is true of the present invention. Such an adjustment mechanism is advantageous and desirable because it enables a user to make an appropriate accurate adjustment between the probe tip and the indicator means in order to establish a desired relationship therebetween. Furthermore, such an arrangement is advantageous because it eliminates the need for having a movable dial indicator face and other relatively complicated mechanisms for zeroing the movable dial pointers including means for holding and/or locking the dial indicator face against further movement at any desired position. Still further, the present construction facilitates replacing probe tips or gaging heads of different ranges on the same gaging device and such construction may also increase the operating range of a particular gaging head. All of the novel features and capabilities made possible by the present adjustment means represent important advancements in the gaging of internal cylindrical surfaces and bores.